Surface Characterization and Electrochemical Properties of Alkyl, Fluorinated Alkyl, and Alkoxy Monolayers on Silicon

Abstract

Alkyl and fluorinated alkyl monolayers covalently bonded to the silicon (111) surface have been prepared by UV illumination of the H-Si(111) surface while immersed in a solution of olefin precursor under high vacuum. An alkoxy monolayer covalently bonded to the silicon (111) surface is formed by the reaction of the H-Si(111) surface with a heated solution of primary alcohol precursors under high vacuum. Ellipsometry, X-ray photoelectron spectroscopy, and atomic force microscopy are used to characterize the three monolayers. The alkyl monolayer is measured to have the largest number of organic adsorbates per surface silicon atom. Properties of the monolayers on the silicon surface are probed by cyclic voltammetry. The hydrophobic alkyl monolayer slows the oxidation of the silicon surface by water. The three monolayers also slow the rate of electron transfer across the silicon-electrolyte interface by acting as a tunneling barrier. The alkyl monolayer in tetrahydrofuran exhibits a large and reproducible blocking of the electron transfer.

Suppression of electron-transfer characteristics of ferrocene by OTS monolayer on a silicon/electrolyte interface

“…In comparison, only few reports are available on the characterization of SAMs on semiconductor surface [25][26][27][28], a system which differs from that of the metal electrode due to the additional space charge layer present on the semiconducting surface. For example, organic thin films formed by the reaction of Grignard reagent with oxide free silicon surface have been recently discussed in terms of an ideal capacitive behavior at silicon electrode/aqueous electrolyte interface [29][30][31]. The electrical characterization of alkyl monolayers on Si/SiO 2 has been discussed in terms of the suppression of charge-carrier tunneling [31].…”

Micro pH Sensors and Biosensors Based on Electrochemical Field Effect Transistors

“…The coverage of modified surface was calculated by using the integrated peak areas of the carbon (1s) and silicon (2p) XPS narrow scans. areal density of the adsorbate to maximum areal density [5,26,27]. The maximum areal densities were adapted to the value of the cross-sectional area of each molecule, which are 18.0 Å 2 (ODMS), 27.5 Å 2 (FAS), and 20.0 Å 2 , respectively.…”

The Integration of Molecular Electronic Devices with Traditional CMOS Technologies

“…The bottom contact was highly doped Si (100), due to its compatibility with CMOS. Because prior to this work most of the monolayer assembly/characterization that had been performed was on Si (111) [16][17][18][19][20][21][22][23], we performed extensive characterization to ensure that the monolayers assembled on Si (100) were comparable in quality to those assembled on Si (111) [24]. Additionally, prior work by our group was performed with a lightly doped Si substrate [16]; however, we have switched to highly (degenerately) doped Si in order to ensure that the electrical characteristics observed from the devices are dominated by inherent molecular properties, rather than depletion in the substrate due to the work function mismatch between the lightly doped bottom Si contact and the Ag top contact [24][25].…”